LET’S GET IT CLEAR
What makes a good positioning belt? Part I: The Anatomy of a belt Let’s start with a reminder that positioning belts are not to be confused with ‘safety’ belts, as used in vehicles, which are made available as restraints. Positioning belts are intended to help position the individual to assist them in postural control and normal dayto-day functions, whereas vehicular restraints are there to restrain the body from flying out of the seat in a traffic accident. The applications, and therefore the designs, are very different for the two different types of belt and should not be confused with each other. Postural support devices (PSDs) are medical devices designed to control body movements, either blocking, minimising, or guiding movements of specific body segments to achieve desired outcomes, while including safety within the seating system. Typical outcomes include increased sitting stability, maintained or corrected posture, increased reach, enhanced propulsion of a mobility
Dr Barend ter Haar has been involved in seating and mobility for over 30 years, including lecturing internationally and developing international seating and decontamination standards.
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In previous issues of THIIS, the Let’s Get it Clear series covered ‘What makes a good cushion?’ over six parts. Equally important components of many seating systems are the postural support devices (PSDs) provided with the seating to complement the cushion and back support elements. This is the first in a series of articles covering PSDs, where we look at the design of different components of a positioning belt to ensure optimal results for the user...
device, or maintenance of a desired seated position for safety purposes (including prevention of falls from the chair). In many cases, the purpose of a PSD can be a combination of one or all of these factors. PELVIC POSITIONING BELTS Before other PSDs (e.g. ankle or shoulder supports) can be issued, the individual will need a pelvic positioning belt and we will therefore be concentrating on these here. Position and control of the pelvis is critical to postural alignment and control and there’s potentially a lot of movement to control. The lowest vertebra in the spinal column, L5, is attached to the top of the pelvis. The pelvis has scope to rotate in three dimensions: posteriorly and anteriorly as viewed from the side; obliquely to the left or right when viewed from the front; and rotationally when viewed from above. All these movements get translated into the spine via the L5 vertebra. Postural reflexes drive people to strive to maintain their centre of gravity within this base of support. Due to the connection of L5 to the top of the pelvis, any change in pelvic position in turn affects the shape of the spinal column. For example, when the pelvis tilts posteriorly, forward flexion tends to occur in the spine leading to a kyphotic posture. When the pelvis rotates obliquely (in the frontal plane), this usually causes lateral flexion of the spine leading to a
scoliotic posture. The positioning of the pelvis is therefore also critical for the alignment of the spine. Some of these ‘asymmetries’ are unavoidable (or ‘fixed’) and, from time-to-time, some are desirable. The important element is to control them appropriately and that is why the selection and placement of flexible PSDs is so important (see BS 86251). The position of the pelvis also greatly changes the distribution of interface pressures between the occupant and any support surfaces, especially the seat cushion and back support. This is an important consideration for the prevention of pressure injuries. A pelvic positioning belt is employed to bring as much control as
